An atom X has a stable ion that is tri-positive.The electronic configuration of the ion is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³. The atomic number & correct electronic configuration of element X is
Correct answer: C. 24, [Ar] 4s¹ 3d⁵
- A. 23, [Ar] 3d⁶
- B. 24, [Ar] 4s² 3d⁴
- C. 24, [Ar] 4s¹ 3d⁵
- D. 25, [Ar] 4s² 3d⁴
Explanation
The stable ion of the element X is tri positive, meaning it has lost three electrons. Given the ion's configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³, adding three electrons back to find the neutral atom gives 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵, which corresponds to the atomic number 24 (element Chromium, Cr) with the configuration [Ar] 4s¹ 3d⁵. Therefore, option C is correct. Options A, B, and D do not match the derived configuration when three electrons are added to the ion's configuration.
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About Electronic Configuration
Electronic configuration describes how electrons occupy shells, subshells and orbitals around an atom. Questions use the Aufbau principle, Pauli exclusion principle and Hund's rule to write configurations, identify valence electrons, form ions and explain periodic trends, including common exceptions such as chromium and copper.
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